1. Field of the Invention
The present invention is directed to a mechanical pencil of the collet-action type whereby a shiftable lead is carried within a collet member and this collet member is maintained in a gripping relationship by the effect of a compression spring and is movable in opposition to the bias of the spring to advance the lead outward from the collet and, more particularly, to the design of such a collet member.
2. Prior Art
A sample embodiment of a mechanical pencil of the above type is shown in FIGS. 4 through 7 of the pending U.S. application, Ser. No. 423,476. This application describes a mechanical pencil with an outer housing having a bore formed along its axis. A collet member is formed by a pair of identically configured mating shells which are maintained in a fixed relation with respect to one another by a cap at one end thereof. The collet member is placed inside the housing bore and the cap extends beyond the housing. It can be depressed against the action of a compression spring from the outside of the housing. The depression and the simultaneous compression of the spring releases an annulus which was forced against a flared end portion of the collet member by the action of the spring, and permits the advancement of the lead. When the end cap is not depressed, the compression spring pulls the collet member into the annulus. Thereby, gripping forces are exerted onto the lead which are sufficient to oppose an individual's writing pressure.
The collet member is inserted into the annulus by axially displacing the collet halfs with respect to one another in such a way that a reduced portion of the collet member mates with the flared portion of this collet member during the insertion process. It is thereby required that both the annulus and the half shells are somewhat elastic, which makes if difficult to provide materials having the requisite sliding properties on the outside and gripping properties on the lead guiding tube side of the collet member as well as good durability of the annulus and the collet member. In addition, the assembly of two deformable members may be quite difficult. It is thus desirable to find a way of producing both the collet halfs and the annulus of non-deformable materials while permitting the placing of the flared portion of the collet member through this annulus, even though the flared portion has an essentially greater diameter than the inner diameter of the annulus.